I find the Millennium regs (which most series seem to base their rules on) to be a little over zealous on the layering question. I've been forced to remove a 3rd layer before - even when it was bloody freezing and pouring with rain.
Before everyone starts crying 'man up!' - I've got less fat on me than a chopstick, so while all the blubber boys are cosy in their natural insulation, I'm half-way to hypothermia
Still, we're rocking into warmer weather now and those Empire groundpounder vests are pretty cosy and prevent the worst of the welts.